In the assembly of electronic components and other such parts on a substrate, where high accuracy in the location alignment is required, an image recognition method has often been employed for detecting the location. Many of the automatic assembly apparatus for electronic components have a built-in image recognition unit for aligning components to a correct location for assembly based on the results of recognition made by the image recognition unit. The image recognition unit comprises an optical system for obtaining an image of the recognition object. Information on location of a recognition object expressed in terms of an optical coordinates system detected by the optical system needs to be converted into information of a mechanical coordinates system maintaining a strict correspondence with the optical information. For conducting a conversion process, offset data representing a relative relationship in the location between the two coordinate systems and a pixel rate, which is a dimensional conversion coefficient between the pixel counts in term of optical coordinates and the actual dimensions in term of mechanical coordinates, are set and registered at the initial stage. In an image recognition unit having a fixed optical system, the initial registration is made at the time when an image recognition unit is incorporated in an automatic assembly apparatus, and does not require any modification in the contents of registration thereafter, unless the optical system is replaced.
In some automatic assembly apparatuses that handle objects different dimensions, for example a die bonder, an image recognition unit often employs a zoom lens system. An appropriate magnification index is determined for the zoom lens system in accordance with the size of a recognition object. In the conventional automatic assembly apparatus, the magnification index is decided by an operator; who determines it watching an object on a monitor screen based on his, or her, intuition and past experience. When the zoom magnification index is changed, the consequence of which is identical to the change of an optical system, the registration of the offset data and the pixel rate and other relevant data has to be renewed at each time. Setting and registration of the magnification index, offset data, and pixel rate, etc., require quite an expertise and work hours. Namely, it has been quite a burden for a line operator, and an improvement in that respect has been looked for.
The present invention addresses the above described problems, and intends to offer an automatic assembly apparatus and the method with which the burden of line operators is alleviated and the quality of operation is improved.